How to get trace ID from code?

Question

I am running a Java application on Google App Engine standard environment.

Looking at the logs (in particular request_log), I can see a couple of interesting IDs such as trace_id and request_id for each request.

Couple of questions:

• How are they different? Are they unique?
• How to obtain them in application code (for the current request)? I would like to log them to a different Stackdriver dataset and be able to correlate the data

Answer 1

In the request handler you can access the headers and pull out X-Cloud-Trace-Context form the HttpServletRequest

@WebServlet(name = "requests", description = "Requests: Trivial request", urlPatterns = "/requests")
public class RequestsServlet extends HttpServlet {
  @Override
  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    req.getHeader("X-Cloud-Trace-Context")
  }
}